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a.core_concepts.md

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Core Concepts (19%)

This covers the API primitives and how to create and configure basic Pods

  • YAML
  • POD
  • ReplicaSet
  • Deployment
  • Namespaces

First of all, make sure to configure kubectl autocomplete, it will easy your life

# BASH

source <(kubectl completion bash) # setup autocomplete in bash into the current shell, bash-completion package should be installed first.
echo "source <(kubectl completion bash)" >> ~/.bashrc # add autocomplete permanently to your bash shell.

# ZSH

source <(kubectl completion zsh)  # setup autocomplete in zsh into the current shell
echo "if [ $commands[kubectl] ]; then source <(kubectl completion zsh); fi" >> ~/.zshrc # add autocomplete permanently to your zsh shell
1. Create a pod with the NGINX image in a namespace called webtier
show 

# Create the namespace if not exist
kubectl get ns
kubectl create ns webtier

# Create the pod
kubectl run nginx --image=nginx --restart=Never -n webtier

==================================================================================================

2. Dry run. Print the corresponding API objects without creating them.

show 

kubectl run nginx --image=nginx --dry-run

==================================================================================================

2. Create the same pod in a namespace called dev using YAML definition file
show 

# Create the namespace if not exist
kubectl get ns
kubectl create ns dev
# An easy way to generate YAML is to use imperactive command with dry-run option
kubectl run nginx --image=nginx --restart=Never -n dev --dry-run -o yaml > nginx-pod.yaml

cat nginx-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}
# Edit the file by adding namespace dev
```yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
namespace: dev
spec:
  containers:
  - image: nginx
    imagePullPolicy: IfNotPresent
    name: nginx
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

# Another way to add namespace dev to the command
kubeclt create -f nginx-pod.yaml -n dev

==================================================================================================

3. Get pods on all namespaces
show 

kubectl get po --all-namespaces

==================================================================================================

4. Start a single instance of hazelcast and let the container expose port 5701 .

show

```bash kubectl run hazelcast --image=hazelcast --port=5701 ```

==================================================================================================

5. Create a busybox pod using kubectl command that runs the command "env". Run it and see the output

show 

kubectl run busybox --image=busybox --command --restart=Never -it -- env # -it will help in seeing the output

# Another way is to run it without -it
kubectl run busybox --image=busybox --command --restart=Never -- env
# and then, check its logs
kubectl logs busybox

==================================================================================================

6. Start a single instance of hazelcast and set environment variables "DNS_DOMAIN=cluster" and "POD_NAMESPACE=default" in the container.

show

```bash kubectl run hazelcast --image=hazelcast --env="DNS_DOMAIN=cluster" --env="POD_NAMESPACE=default" ``` ``` # Verify it via kubectl logs hazelcast ```

==================================================================================================

7. Using kubectl command, create a pod using busybox image, set env value var1=val1. Verify the existance of the env inside the pod

show 

# This is an easy way
kubectl run busybox --image=busybox --restart=Never --env=var1=val1 -it -- env


# Another way is to run it without -it
kubectl run busybox --image=busybox --restart=Never --env=var1=val1
# and then
kubectl exec -it busybox -- env
# or
kubectl describe po busybox | grep val1

==================================================================================================

8. Using kubectl command, create a pod using nginx image, set env value var2=val2, print it and make sure the pod is automatically deleted after it's completed.

show 

kubectl run nginx --image=nginx --restart=Never --env=var2=val2 -it  --rm -- env

9. perform the pervious task using YAML file definition

==================================================================================================

Start a single instance of nginx, but overload the spec of the deployment with a partial set of values parsed from JSON.

show 

kubectl run nginx --image=nginx --overrides='{ "apiVersion": "v1", "spec": { ... } }'

==================================================================================================

10. Create a busybox pod that echoes 'hello world' and then exits

show 

kubectl run busybox --image=busybox -it --restart=Never -- echo 'hello world'
# Another way
kubectl run busybox --image=busybox -it --restart=Never -- /bin/sh -c 'echo hello world'

==================================================================================================

11. Using kubectl command to get YAML definition file for creating a namespace call production
show 

kubectl create ns production --dry-run -o yaml

==================================================================================================

12. Using kubectl command, create a pod using kubectl command that uses perl to calculate pi to 2000 digits, then stops and print the output
show 

kubectl run pi --image=perl --restart=OnFailure --dry-run -- perl -Mbignum=bpi -wle 'print bpi(2000)' 

kubectl logs pi

==================================================================================================

12. Start the cron job to compute π to 2000 places and print it out every 5 minutes.
show 

kubectl run pi --schedule="0/5 * * * ?" --image=perl --restart=OnFailure -- perl -Mbignum=bpi -wle 'print bpi(2000)' 

kubectl logs pi

==================================================================================================

13. Get the YAML for a new ResourceQuota called 'myrq' without creating it
show 

kubectl create resourcequota myrq -o yaml --dry-run

==================================================================================================

14. Change pod's image to nginx:1.7.1. Observe that the pod will be killed and recreated as soon as the image gets pulled
show 

# kubectl set image POD/POD_NAME CONTAINER_NAME=IMAGE_NAME:TAG
kubectl set image pod/nginx nginx=nginx:1.7.1
kubectl describe po nginx # you will see an event 'Container will be killed and recreated'
kubectl get po nginx -w # watch it

==================================================================================================

15. Get the pod's ip, use a temp busybox image to wget its '/'
show 

kubectl get po -o wide # get the IP, will be something like '10.1.1.131'
# create a temp busybox pod
kubectl run busybox --image=busybox --rm -it --restart=Never -- sh
# run wget on specified IP:Port
wget -O- 10.1.1.131:80
exit

==================================================================================================

16. Get this pod's YAML without cluster specific information
show 

kubectl get po nginx -o yaml --export

==================================================================================================

17. Get information about the pod, including details about potential issues (e.g. pod hasn't started)
show 

kubectl describe po nginx

==================================================================================================

18. Get pod logs
show 

kubectl logs nginx

==================================================================================================

If pod crashed and restarted, get logs about the previous instance
show 

kubectl logs nginx -p

==================================================================================================

19. Connect to the nginx pod
show 

kubectl exec -it nginx -- /bin/sh

==================================================================================================

Start a single instance of hazelcast and set labels "app=hazelcast" and "env=prod" in the container.

show 

kubectl run hazelcast --image=hazelcast --labels="app=hazelcast,env=prod"

==================================================================================================

Start a replicated instance of nginx.

show 

kubectl run nginx --image=nginx --replicas=5

10. perform the pervious task using YAML file definition

==================================================================================================

11. Start a single instance of nginx, but overload the spec of the deployment with a partial set of values parsed from JSON.
show 

kubectl run nginx --image=nginx --overrides='{ "apiVersion": "v1", "spec": { ... } }'

==================================================================================================

12. Create a busybox pod that echoes 'hello world' and then exits
show 

kubectl run busybox --image=busybox -it --restart=Never -- echo 'hello world'
# Another way
kubectl run busybox --image=busybox -it --restart=Never -- /bin/sh -c 'echo hello world'

==================================================================================================

13. Using kubectl command to get YAML definition file for creating a namespace call production
show 

kubectl create ns production --dry-run -o yaml

==================================================================================================

15. Using kubectl command, create a pod using kubectl command that uses perl to calculate pi to 2000 digits, then stops and print the output
show 

kubectl run pi --image=perl --restart=OnFailure --dry-run -- perl -Mbignum=bpi -wle 'print bpi(2000)' 

kubectl logs pi

==================================================================================================

16. Start the cron job to compute π to 2000 places and print it out every 5 minutes.
show 

kubectl run pi --schedule="0/5 * * * ?" --image=perl --restart=OnFailure -- perl -Mbignum=bpi -wle 'print bpi(2000)' 

kubectl logs pi

==================================================================================================

17. Get the YAML for a new ResourceQuota called 'myrq' without creating it
show 

kubectl create resourcequota myrq -o yaml --dry-run

==================================================================================================

18. Change pod's image to nginx:1.7.1. Observe that the pod will be killed and recreated as soon as the image gets pulled
show 

# kubectl set image POD/POD_NAME CONTAINER_NAME=IMAGE_NAME:TAG
kubectl set image pod/nginx nginx=nginx:1.7.1
kubectl describe po nginx # you will see an event 'Container will be killed and recreated'
kubectl get po nginx -w # watch it

==================================================================================================

19. Get the pod's ip, use a temp busybox image to wget its '/'
show 

kubectl get po -o wide # get the IP, will be something like '10.1.1.131'
# create a temp busybox pod
kubectl run busybox --image=busybox --rm -it --restart=Never -- sh
# run wget on specified IP:Port
wget -O- 10.1.1.131:80
exit

==================================================================================================

20. Get this pod's YAML without cluster specific information
show 

kubectl get po nginx -o yaml --export

==================================================================================================

21. Get information about the pod, including details about potential issues (e.g. pod hasn't started)
show 

kubectl describe po nginx

==================================================================================================

22. Get pod logs
show 

kubectl logs nginx

==================================================================================================

23. If pod crashed and restarted, get logs about the previous instance
show 

kubectl logs nginx -p

==================================================================================================

24. Connect to the nginx pod
show 

kubectl exec -it nginx -- /bin/sh

==================================================================================================

25. Start a single instance of hazelcast and set labels "app=hazelcast" and "env=prod" in the container.
show 

kubectl run hazelcast --image=hazelcast --labels="app=hazelcast,env=prod"

==================================================================================================

26. Start a replicated instance of nginx.
show 

kubectl run nginx --image=nginx --replicas=5